a) Field of the Invention
The present invention generally relates to audio systems and more particularly to systems for enhancing the sound received by transient individuals located at discrete locations distanced from a primary loudspeaker system. The subject audio system permits transient individuals to roam within a predetermined area without overly detracting from the sound quality delivered to these individuals.
b) Description of Related Art
The current state of the art for sound reproduction or sound supporting equipment used in concert halls or in other indoor and outdoor spaces entails the use of one or more loudspeaker cluster locations. These locations are typically located at or near the physical location of the actual sound source or that of the virtual sound source. Unfortunately, the acoustical sound reproduction quality of such conventional systems is detrimentally effected by distortion of the frequency and time spectrum resulting from the distances travelled by the sound. Also, non-linear type distortions are introduced due to the physics of the air compression and rarifactions by which the sound propagates. Moreover, since the perceived loudness and sound pressure level decreases in proportion to the distances travelled from the sound source, in order to achieve the desired sound pressure level at remote listener positions substantially more sound pressure must be developed at the source. However, increasing sound pressure level at these discrete locations produces increased distortion.
Persons attending concerts, shows, or speaking engagements in large halls or arenas (indoor as well as outdoor) are becoming more demanding in their desires for high quality sound; they want to have the sound quality delivered to their specific location by public address systems which mimic recording studio quality or at least mimics the sound quality at the main loudspeaker's mixer board. One common approach taken by sound system designers is to utilize "delayed speaker systems" in combination with the main loudspeaker system. In particular, additional loudspeakers are provided at remote locations in order to direct quality sound reproduction to individuals who are poorly positioned to receive sound from the main loudspeaker system. These fixed remote loudspeakers typically have their input signals delayed in time with respect to signals provided to the main loudspeaker systems to synchronize their acoustic output with the sound arriving from the main loudspeaker system; this approach reduces echo and feedback which results from two sound sources which are offset in distance. However, these fixed remote loudspeakers fail to properly serve transient individuals.
In an attempt to provide an enhanced audio system, U.S. Pat. No. 5,432,858 to Clair, Jr., et al. teaches a audio system comprising a wireless transmitter and plural augmented sound reproducing systems. Each sound subsystem is a portable unit arranged to be carried by a person located at a remote position with respect to the main loudspeaker. Each sound subsystem includes a receiver for receiving a broadcast signal, and a microphone positioned on a headset to detect sound arriving from the main loudspeakers. The sound subsystem further includes circuitry which augments this broadcast signal to thereby synchronize the broadcast signal with the sound arriving from the main loudspeakers. In order to augment the broadcast signal in accordance with the teaching of this patent, the subsystem uses a delay circuitry provided in the subsystem headphone set which delays the broadcast signal received by the receiver for a predetermined period of time which generally corresponds to the time it takes for the sound arriving from the main loudspeakers to propagate through the air to the remote location of the headset.
The sound augmentation system disclosed by U.S. Pat. No. 5,432,858 takes one of three forms: a "zone" system, a "manually synchronized" system, and a "self-synchronized" system. For the "zone" system, the audience is broken into discrete zones, which encompass a known distance from the main sound source. Each listener located within a given zone receives augmented sound from a particular receiver/transducer subsystem delayed a predetermined time. Accordingly, the augmented sound and the main sound arrive at the ears of each listener within that zone in substantial synchronism. More particularly, audience members within each zone personally tune their respective receiver to the appropriate channel for their zone, to thereby listen to the sound reproduced by the associated remote transducer in substantial synchronism with the main arriving sound. However, each person attending a concert where the "zone" system of this invention is in use must be given instructions on how and why to tune his/her receiver/amplifier unit to a particular channel setting based on that individual's location. It will be understood by anyone familiar with typical concert environments, however, that such a system will be overly complicated and impractical to distribute and use. Moreover, this system overly limits the portability of the audio system because the "zone" system requires the user to manually tune his/her receiver during movement about the arena.
The second "manually synchronized" system of U.S. Pat. No. 5,432,858 is even more limiting than the "zone" system described above. The "manually synchronized" system requires the listener to manually adjust his/her time delay circuitry. With this arrangement, the entire audience is covered by a single transmitter zone, wherein the audio signal is broadcast over a single frequency by a common, single wireless transmitter to all of the receiver/transducer subsystems located throughout the concert hall. It will again be understood by anyone familiar with typical concert environments, however, that such a "manually synchronized" system will be overly complicated and impractical to both distribute and use.
The third "self-synchronized" system of U.S. Pat. No. 5,432,858 accomplishes synchronization of the broadcast signal and the sound arriving from the main loudspeakers by providing a sampling microphone on the portable transducer unit. The circuitry of the portable transducer unit automatically adjusts the time delay in response to the sound picked up by the sampling microphone. This "self-synchronized" system suffers from the drawback in that it requires overly complex, costly and bulky circuitry. Specifically, the receiver/amplifier unit requires a wireless receiver, signal dynamics processor with a gating circuit, a programmable control signal delay circuit, a signal gate, a microphone preamplifier, a summing circuit, and a signal correlation circuit. The signal correlation circuit itself comprises a correlate circuit and a controller. Of course, the sampling microphone is inherently susceptible to background ambient noise, and thus require further means to disable the microphone when not in the presence of the main arriving sound.
While the foregoing approaches to achieve sound enhancement have some aural benefits, these conventional systems nevertheless suffer from numerous drawbacks resulting from decreased sound quality being delivered to remote listeners. These systems also limit the listener to specific listening areas, thus do not satisfy the listening needs of a mobile audience. Moreover, the prior art systems result in relatively complex, unwieldy and inflexible sound reproduction systems. Thus, the resulting size, weight and cost of these prior art receivers are preclusive.
Accordingly, the need exists for an audio enhancement system which overcomes the disadvantages of the prior art.